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Discussion Starter #1
We have a '98 R72 and is has always been under horse powered I thought. We have to keep RPM up by pulling back on the hydro and we struggle all the time. I've always felt we were 100 hp short. Long story on the last day of harvest this fall we found we only had 100 psi fuel pressure on the rail at normal engine load and if we pushed it as hard as we could it would go to 115-120. From what we could find out we should be 150 psi under normal engine load and raise to 175 under heavy load. In the past 3-4 years we've had pump rebuilt, all new injectors, checked for air leaks, put an electric charge pump at fuel tank to pump fuel back to the engine and replaced fuel shut off solenoid. We've cleaned and check the check valves in the fuel lines on the engine. We've ran the machine for 5 years and it's never had HP. We are going to have a cummins tech work on it this spring before wheat. We had another cummins tech look at it this fall and he was more of sham type person than really wanting to fix it. That's another story. Any one have any ideas what could be causing low fuel pressure?
 

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Spring loaded relief valve, that allows the fuel to return to the tank may be weak... i had that issue on my C15 cat..

Going from 550 to 650 hp (ecm numbers only) when pulling hard it would miss. I had the lift pump replaced and the pressure regulator also replaced. The cat would push fuel and the spring loaded regulator held back proper pressure to fuel the injectors. Sounds like you have replaced everytjing else... not familure with what the cummins does, not like the old 855s anyways.
 

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Providing pump is good I would switch the fuel pressure sender. This sender will look good when cummins is hooked up to it when indeed it is bad. I usually send ECM in with pump to have them be sure it is completely up to date and set proper for the application. PFP may have box to plug in and give you more yet.
 

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I don't see any mention of the charge air pressure, you might be looking in the complete wrong direction. I would build a plug for the intake side of the charge air cooler and hookup to an air compressor and regulator and build air pressure to about 40 psi and look for leakage. Can you hear the turbo? If so you probably have a substantial leak. The engine won't smoke because if it is electronic it monitors charge air pressure and cuts back on the fuel. Low boost pressure = low fuel pressure...
 

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flow checks and pressure checks, leak checks on pressure regulating controls, demand vs delivered rail pressure, and yes proper calibration of sensors.. these are the basics that insite program through cummins will have your tech check. m elemons as we refer to them, were not the worst design, but they have their issues. sensors are one of them as well as the gear pump. you have covered a lot of this already so make sure the tech hooks up the inline adapter and the laptop and follows all the tests. he will need the adapters and hoses and orifices to do it properly.
 

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Discussion Starter #7
I rigged up a boost gauge this fall and had it right outside the cab. 24 pounds is high as I ever saw it when engine was loaded. It would run 15-20 most of the time. I never could find anyone who could tell me what it should be. The tech who we had looking at it said that was "about right".
 

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Rule of thumb is 1 PSI boost for each 10 HP at or near MAX HP as long as there is no wastegate. I do not recall the M11 having a wastegate. I don't believe the what I call dumb electronic M11 Gleaner used has any sensor that cares about boost pressure. If it was a step up Cummins it would have the smarter engine with more electrics taking care of functions
 
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